The suppression of fat signals is an important component of many MRI exams in the clinic. Signals from fat that resonate at different frequencies compared with water need to be suppressed to obtain high quality images. The prevalence of chemical shift artifacts become higher with increasing magnetic field strengths and the suppression of fat resonances becomes increasingly complicated.
Techniques aimed at suppressing fat take advantage of the two characteristic differences in the behavior of water and fat, either the difference in relaxation times or chemical shift effects. In general, approaches that are used to achieve fat signal suppression consist of the application of pre-pulses, so called fat saturation (FS) or inversion recovery (IR) pulses, that result in nulling of the fat signals prior to the MRI imaging sequence, or by the use of specific radiofrequency (RF) excitation pulses that are water selective, such as in the case of binomial 1-1 RF excitation pulse schemes, the so-called water selective water excitation (WE). In general these methods are sensitive to magnetic field inhomogeneities, imperfect RF saturation or inversion pulses, or limited by the magnetization recovery time (T1) of the fat protons.
The following papers explore selective signal suppression using two consecutive binomial off-resonant rectangular (BORR) pulses with a phase difference of π. Ye et al. (2014). Robust selective signal suppression using binomial off-resonant rectangular (BORR) pulses. Journal of Magnetic Resonance Imaging, 39(1), 195-202. doi: 10.1002/jmri.24149 and Ye et al. (2015). Retrobulbar magnetic resonance angiography using binomial off-resonant rectangular (BORR) pulse. Magn Reson Med, 74(4), 1050-1056. doi: 10.1002/mrm.25498. The results presented herein will be discussed in more detail later.
Hence, an improved method for reducing MR signals originating from fat in MR imaging would be advantageous, and in particular a method that is less sensitive to magnetic field inhomogeneities would be advantageous.